Again, there were few media reports of this incident (although I've seen one or two), and my only explanation comes from an experienced EMT, whose emergency services buddies said an LP tank at the Pentagon exploded at that time (BTW, they also said the airplane hit the ground before hitting the Pentagon).
I was 3.5 miles from the Pentagon at the time, your friend in Foggy Bottom was 2 miles away. So there's no doubt that if I heard it from 3.5 miles, that she also would have heard it from 2 miles.
And I don't at all dispute that her house shook, because I could actually "feel" the explosion as much as hear it. Again, the windows visibly shook.
BTW, I reported seeing smoke on FR that morning, and I initially couldn't tell exactly where it was coming from. It's very possible I posted just before leaving the house right around 10AM, and it's also possible I would have said the smoke was in the direction of the Mall. So your source may have been me!